The global campaign to eradicate polio has changed tactics to focus on the most susceptible nations and cut back on immunization elsewhere. The change in approach is the result both of success containing the disease and a shortage of money.

Fifteen years after the polio campaign began, more than two billion children have been immunized against it. The number of cases has dropped from 350,000 in 125 countries to under 2,000 last year in only seven countries.

Ninety-nine percent of the patients are in just three of them: India, Nigeria and Pakistan. World Health Organization official Gina Tambini says the disease also remains endemic to a lesser extent in Egypt, Afghanistan, Niger and Somalia.

"This is the lowest number of endemic countries in history," said Ms. Tambini. "Never before has polio been as geographically contained as it is now."

Because polio remains persistent in these nations, the Polio Eradication Initiative is shifting its resources to them and to six more countries considered at high risk of re-infection because of low vaccination rates and proximity to ravaged areas. These six are Angola, Bangladesh, Democratic Republic of Congo, Ethiopia, Nepal and the Sudan. Altogether, the 13 nations will receive nearly 300 million oral polio vaccine doses and $35 million previously intended for other regions.

But campaign officials admit that the new strategy creates risks for countries where polio immunization is being reduced. Robert Keegan of the U.S. government's Centers for Disease Control, a partner in the project, says countries free of the virus risk importing it if proper protections are not maintained. He points out that Lebanon, Bulgaria, China, Ghana and other countries recently got cases from India and Nigeria.

"The risk of importation is relatively small considering the number of cases we face every year," said Mr. Keegan. "But as we make this strategic shift, it becomes critical to ensure rapid response capacities in place to rapidly control imported polioviruses. Therefore, to further minimize the risk, we will be maintaining high surveillance for potential outbreaks in all countries, and we'll be improving routine immunization services as well."

Polio eradication campaign officials concede that they would continue their program in some other areas bordering endemic regions if they had more money. At the United Nations Children's Fund UNICEF, Dr. Yves Bergevin says the campaign needs an additional $275 million through the end of next year to meet its goals.

"So while we are very near the end, there is a tremendous challenge ahead of us and a real risk that if we don't do this right over the next few years, we may have difficulty finishing the job," said Dr. Bergevin.

The private membership organization Rotary International, another campaign partner, is raising $80 million and hopes the rest will come from other donor groups and nations.

As part of the new polio immunization strategy, the number of vaccination rounds will increase in India, the hardest hit country. Campaign officials say that, because of progress, they mistakenly reduced the number of rounds in the past two years. But this caused a six-fold increase in new cases, including in some polio-free parts of India.